1. Field of the Invention
The present invention relates to an apparatus and a method for heating a protective member for protecting a fusion splicing part of optical fibers.
2. Description of the Related Art
Two coated optical fibers are permanently spliced to each other in such a manner that a coating layer of an end part of each coated optical fiber is removed to expose a vitreous fiber thereof(hereinafter referred to xe2x80x9coptical fiberxe2x80x9d), and the thus exposed optical fibers are aligned, joined end to end and fusion spliced together. The exposed portion of the optical fibers including the fusion splicing part is covered with a protective member and protected thereby. FIGS. 8 and 9 are diagrams showing protective members each used for the optical fiber fusion splicing part. FIGS. 8A and 9A are transverse sectional views of the protective members, and FIGS. 8B and 9B are longitudinal sectional views of the same.
In FIGS. 8 and 9, reference numerals 10 and 10xe2x80x2 represent protective members; 11 and 11xe2x80x2, adhesive tubes; 12 and 12xe2x80x2, reinforcing members; and 13, a thermal shrinking tube. The protective member 10 of FIG. 8 is applied mainly to a splicing part of the optical fiber ribbon containing a plurality of optical fibers. The protective member 10xe2x80x2 of FIG. 9 is applied mainly to a splicing part of a coated optical fiber containing a single optical fiber.
The protective member 10 of FIG. 8 consists of the thermal shrinking tube 13, the adhesive tube 11 and the reinforcing member 12 which is solid semicircular in cross section. The adhesive tube 11 and the reinforcing member 12 are stored in the thermal shrinking tube 13 while the reinforcing member 12 is disposed in parallel to the adhesive tube 11 in a longitudinal direction. The protective member 10xe2x80x2 of FIG. 9 consists of the thermal shrinking tube 13, the adhesive tube 11xe2x80x2 and the reinforcing member 12xe2x80x2 which is solid circular in cross section. The adhesive tube 11xe2x80x2 and the reinforcing member 12xe2x80x2 are stored in the thermal shrinking tube 13 while the reinforcing member 12xe2x80x2 is disposed in parallel to the adhesive tube 11xe2x80x2 in a longitudinal direction. The adhesive tubes 11 and 11xe2x80x2 are made of adhesive resin, such as ethylene vinyl acrylate. The reinforcing members 12 and 12xe2x80x2 are made of material having good heat resistance and a high compressive strength, such as glass ceramic or stainless steel. The thermal shrinking tube 13 is made of irradiated polyethylene, for example.
An optical fiber ribbon containing a plurality of optical fibers is made in such a manner that a plurality of optical fibers are aligned and coated by a coating resin to form a tape-shape. As shown in FIG. 8, the reinforcing member 12 is shaped to be solid semicircle in cross section, and the adhesive tube 11 is shaped to be hollow elliptical in cross section, in order to dispose the optical fiber ribbon thereto easily. However, the adhesive tube 11 may be hollow circular in transverse cross section, since it is soft and easy to be deformable. In the case of a coated optical fiber containing a single optical fiber, the cross section of the coated optical fiber is circular, and hence, there is no need that the reinforcing member 12xe2x80x2 should be solid semicircular in cross section. Therefore, as shown in FIG. 9A, the reinforcing member 12xe2x80x2 is solid circular in cross section, which makes it easy to manufacture of the reinforcing member, and the adhesive tube 11xe2x80x2 is also hollow circular in cross section.
FIG. 10 shows a working procedure to protect an optical fiber fusion splicing part with the thus produced protective member. FIGS. 10A, 10B and 10C are longitudinal sectional views showing the working procedure. In FIG. 10, constituent parts same as those in FIGS. 8 are referenced correspondingly, and their description will be omitted. In FIG. 10, reference numeral 14 represents an optical fiber ribbon; 15, an optical fiber; and 16, a fusion splicing part.
As shown in FIG. 10A, two optical fiber ribbons are spliced to each other in such a manner that a coating layer of an end part of each optical fiber ribbon is removed to expose optical fibers thereof, and the thus exposed optical fibers are aligned, joined end to end and fusion spliced together. The exposed portion of the optical fibers 15 including the fusion splicing part 16 is passed through the adhesive tube 11 of the protective member 10. A plurality of optical fibers 15 are aligned in parallel in the direction vertical to the paper of the drawing. Accordingly, the optical fibers 15 are seen as a single optical fiber in FIG. 10.
Subsequently, the fusion splicing part of the optical fibers, which is covered with the protective member 10, is disposed on a heater of a heating apparatus and heated thereby. By the heating, the adhesive tube 11 is fused, and also the thermal shrinking tube 13 is thermally shrunk. A compressive force of the thermal shrinking tube 13 generated due to thermal shrunk puts the fusion splicing part of the optical fibers adaptively along the reinforcing member 12. The inside of the thermal shrinking tube 13 is filled with the fused adhesive resin of the adhesive tube 11.
FIG. 11 shows an embodiment of a heater of a heating apparatus which is used for heating the protective member. FIG. 11A is a plan view showing the heater, and FIG. 11B is a longitudinal sectional view taken on line Xxe2x80x94X in FIG. 11A. FIG. 11C shows a graph of a temperature distribution of the heater. The heater designated by reference numeral 17 is a ceramic heater in which a heating conductive circuit 17a is buried in a narrow ceramic plate 17b. The heater 17 has a temperature distribution configured such that temperature at the center of the heater is high and gradually decreases toward both sides ends of the heater as shown in FIG. 11C. That is, when the heater is operated, the protective member 10 is heated gradually from the center to both side ends.
FIG. 10B shows the protective member when its center is heated. FIG. 10C shows the protective member when the heating reaches both side ends of the protective member. As shown in FIG. 10B, with the heating of the heater, at first, a central portion of the adhesive tube 11 is fused, while the central portion of the thermal shrinking tube 13 shrinks. Subsequently, the phenomena of the fusing of the adhesive tube and the shrinking of the thermal shrinking tube gradually progress toward both side ends of the protective member. Finally, the adhesive tube is fused over the entire length of the protective member and the thermal shrinking tube is also shrunk over the entire length as shown FIG. 10C.
During this process, the phenomenon of fusing of the adhesive tube progresses from the center to both the side ends and therefore air around the central portion of the fusion splicing part of the optical fibers is extruded towards both the side ends of the protective member. If the air is completely extruded from the center to both the side ends, there is no fear that the air around the optical fiber fusion splicing part. remains in the form of air bubbles in the adhesive resin.
If the phenomenon of the heating of the protective member does not progress from the center toward both the side ends gradually and the portions near both side ends is heated excessively quickly, the air is not completely extruded to both the side ends and sometimes remains in the form of air bubbles in the adhesive resin. In such a case that air bubbles remain in the vicinity of the optical fiber fusion splicing part, the following problem arises. When the optical fiber fusion splicing part protected by the protective member undergoes a variation of ambient temperature, the air in the bubbles expands and shrinks to generate a bending stress in the optical fiber. This leads to deterioration of the transmission characteristic of the optical fiber. Accordingly, it is important that the protective member is gradually heated from the center to both side ends.
The produce and protection of the optical fiber fusion splicing part described above are carried out by using mainly a fusion splicing apparatus and a heating apparatus for heating the protective member. In general, the heating apparatus, which is assembled to the housing of the fusion splicing apparatus, is used. In order to splice the optical fibers, first of all, the heating apparatus, a stripping tool, a fiber cutting tool, a protective member and the like are transported to a site where coated optical fibers are laid. In the site, the following work is done in the order of removing a coating layer of an end of each optical fiber, cutting the optical fibers, fusion splicing the optical fibers, applying a protective member to the fusion spliced optical fibers, and heating the protective member.
In the heating process of the protective member, a heating apparatus with the above-mentioned heater is used. A portion including the optical fiber fusion splicing part covered with the protective member is laid along the heater and then heated thereby. The adhesive tube stored in the protective member is fused while the thermal shrinking tube is shrunk. Accordingly, the protective member is fixed to the optical fiber fusion splicing part while covering it.
In a usual heating process, work to apply a protective member to an optical fiber fusion splicing part, work to set the protective member in a heating apparatus by laying it along a heater of the heating apparatus, and work to take the heated protective member out of the heating apparatus are all done by manual. During a period from the setting of the object to be heated in the heating apparatus to the taking the heated object out of the apparatus, a control circuit of the heating apparatus automatically performs the operations of feeding current to the heating conductive circuit of the heater, keeping heater temperature, stopping the heating operation after the heater temperature is kept for a predetermined period of time, and cooling it to about ambient temperature.
The period from the setting of the object to be heated in the heating apparatus to the taking the heated object out of the apparatus is needed from 100 to 150 seconds although it depends on a kind of the optical fiber ribbon since the size of the protective member depends on the number of optical fibers of the optical fiber ribbon. A worker for splicing fibers must wait during this period, and can not do any other work during the period. Accordingly, it is required that the time taken for the heating and cooling is as short as possible.
Since the heating apparatus is usually assembled into the housing of the fusion splicing apparatus, an electric power of the heating apparatus is supplied from a power supply which supplies electric power to the fusion splicing apparatus. Therefore, voltage and current must be kept within limits. In the usual fusion splicing apparatus, the voltage that may be used for the heating apparatus is limited within DC 12V and the electric power is within about 32 W. Therefore, resistance of the heater of the heating apparatus is 4.5 xcexa9 in lower limit, and a heater of which resistance is smaller than 4.5 xcexa9 can not be used. Further, the electric power for energizing the heater cannot be further increased in order to reduce the time taken for the heating and cooling.
Accordingly, an object of the present invention is to provide an apparatus and a method for heating a protective member for protecting a fusion splicing part of optical fibers. The apparatus and method are capable of reducing the time taken for the heating process without increasing the heating power of the heating apparatus.
The above-mentioned object can be achieved by a heating apparatus for heating a protective member for a fusion splicing part of optical fibers. The apparatus comprises a heater including a plate-shaped member which is made of heat-resistive and insulated material and has an elongated shape extending in a longitudinal direction, a first heating conductor pattern disposed in a central portion of the plate-shaped member in the longitudinal direction, and a second heating conductor pattern disposed in both end portions of the plate-shaped member in the longitudinal direction. In the heating apparatus, the first heating conductor pattern and the second heating conductor pattern are independently controlled their temperatures.
In the above-mentioned heating apparatus, it is preferable that the second heating conductor pattern extends from one end portion of the plate-shaped member to the other end portion thereof in the longitudinal direction. It is also preferable that the second heating conductor pattern comprises two heating conductor patterns which are separately disposed in each end portion of the plate-shaped member in the longitudinal direction while being close to an end of the first heating conductor pattern or overlapping with the first heating conductor pattern. The two heating conductor patterns may be preferably disposed symmetrical with respect to the center of the plate-shaped member.
Further, it is preferable that the first and second heat conductor patterns have same resistance value.
Moreover, it is preferable that the plate-shaped member comprises a first plate-shaped member in which the first heating conductor pattern is disposed and a second plate-shaped member in which the second heating conductor pattern is disposed. In such a heater with two plate-shaped members, it is preferable that the first and the second heating conductor patterns are printed on the first and the second plate-shaped members respectively, and the first and second plate-shaped members are arranged in parallel while a spacer is disposed therebetween. It is also preferable that the first and second heating conductor patterns are buried in the first and second plate-shaped members respectively, and the first and second plate-shaped members are combined to form the heater.
Current is first fed to the first heating conductor pattern disposed in the central portion of the heater by use of the heating apparatus of the invention to thereby heat the central portion of a protective member. Since the first heating conductor pattern is small in area and hence its heat capacity is small, temperature in the central portion of the heater quickly rises, so that a temperature rise time is reduced for a fixed consumption of the electric power. Subsequently, the current being fed to the first heating conductor pattern is stopped, and current is fed to the second heating conductor patterns disposed at least in both end portions, to thereby heat both end portions of the protective member. In this case, both end portions are heated by the remaining heat of the first heating conductor pattern and the heat of second heating conductor pattern. Further, since the center of the protective member is not heated excessively while the both end portions of the protective member is heated by the second heating conductor, cooling of the heated object is quick. Accordingly, the whole heating time may be reduced by about 20%.
Further, in the above-mentioned heating apparatus, it is preferable that a first temperature sensor and a second temperature sensor are respectively provided near the first heating conductor pattern and the second heating conductor pattern to detect temperatures thereof, and a control mechanism is provided to control, on the basis of temperatures detected by the first or second temperature sensor respectively, temperatures of the first and second heating conductor patterns separately so that the temperatures of the first and second heating conductor patterns are kept at predetermined temperatures for a predetermined time.
By the control, the phenomena of the fusing of the adhesive tube and the shrinking of the thermal shrinking tube gradually progress toward both side ends of the protective member, from the center thereof. Therefore, there is no fear that the air around the optical fiber fusion splicing part remains in the form of air bubbles in the adhesive resin.
Further, it is preferable that an ambient temperature sensor is attached to a location separated from the heater to such an extent that it is not influenced by the heater temperature, and a control mechanism is provided to control, on the basis of a temperature detected by the ambient temperature sensor, temperatures of the first and second heating conductor patterns so that temperatures of the first and second heating conductor patterns are kept at given values independent of ambient temperature.
A current fed to the heating conductor pattern is controlled in accordance with an ambient temperature detected by the ambient temperature sensor so that heating temperatures of the first and second heating conductor patterns are invariable irrespective of a variation of the ambient temperature. Accordingly, the heating of the protective member is made uniform independent of the ambient temperature.
Moreover, it is preferable that the above-mentioned heating apparatus comprises a heating chamber, clamping member and a cover. With the heating chamber, the heater can be secured. With the cover attached to the heating chamber, it is possible to close the heating chamber to thereby confine the heat within the heating chamber.
Further, the above-mentioned object can be achieved by a method of heating a protective member for protecting a fusion splicing part of optical fibers, the heating method comprising the steps of:
putting a protective member covering with an optical fiber fusion splicing part along a heater, the heater including a plate-shaped member which is made of heat-resistive and insulated material and an elongated shape extending in a longitudinal direction, a first heating conductor pattern disposed in a central portion of the plate-shaped member in the longitudinal direction, and a second heating conductor pattern disposed in both end portions of the plate-shaped member in the longitudinal direction;
heating the first heating conductor pattern to be a predetermined temperature;
keeping the predetermined temperature of the first heating conductor pattern for a predetermined time;
stopping the heating of the first heating conductor pattern;
heating the second heating conductor pattern to be a preset temperature;
keeping the preset temperature of the second heating conductor pattern for a preset time;
stopping the heating of the second heating conductor pattern to return a temperature of the optical fiber fusion splicing part covered with the protective member to ambient temperature.